Flat heat pipe and method for manufacturing the same

ABSTRACT

An exemplary flat heat pipe includes a hollow tube and a wick structure lining an inner surface of the tube. The tube includes an evaporator section, an adiabatic section and a condenser section defined in turn along a longitudinal direction thereof. The wick structure includes a first wick portion located in the evaporator section, a second wick portion located in the condenser section, and a third wick portion extending longitudinally from the evaporator section, through the adiabatic section to the condenser section and communicating with the first wick portion and the second wick portion. A capillary force of the first wick portion is larger than that of the third wick portion, and a pore density of the first wick portion is less than that of the third wick portion.

BACKGROUND

1. Technical Field

The disclosure generally relates to heat transfer apparatuses such asthose used in electronic equipment, and more particularly to a flat heatpipe with stable and reliable performance.

2. Description of Related Art

Heat pipes are widely used in various fields for heat dissipationpurposes due to their excellent heat transfer performance. One commonlyused heat pipe includes a sealed tube made of thermally conductivematerial with a working fluid contained therein. The working fluidconveys heat from one end of the tube, typically referred to as anevaporator section, to the other end of the tube, typically referred toas a condenser section. Preferably, a wick structure is provided insidethe heat pipe, lining an inner wall of the tube, and drawing the workingfluid back to the evaporator section after it condenses at the condensersection.

During operation of the heat pipe in a typical application, theevaporator section of the heat pipe maintains thermal contact with aheat-generating electronic component. The working fluid at theevaporator section absorbs heat generated by the electronic component,and thereby turns to vapor. The generated vapor moves, carrying the heatwith it, toward the condenser section. At the condenser section, thevapor condenses after the heat is dissipated. The condensate is thendrawn back by the wick structure to the evaporator section where it isagain available for evaporation. For the condensate to be drawn backrapidly, the wick structure located at the evaporator section must havea capillary force larger than that of the wick structure located at thecondenser section. However, the capillary force of the wick structure isuniform. Thus, the evaporator section is prone to become dry.

What is needed, therefore, is a heat pipe to overcome the abovedescribed shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal, cross-sectional view of a flat heat pipeaccording to a first embodiment of the present disclosure.

FIG. 2 is a transverse, cross-sectional view of an evaporator section ofthe flat heat pipe of FIG. 1, corresponding to line II-II thereof.

FIG. 3 is a transverse, cross-sectional view of a condenser section ofthe flat heat pipe of FIG. 1, corresponding to line thereof.

FIG. 4 is a longitudinal, cross-sectional view of a flat heat pipeaccording to a second embodiment of the present disclosure.

FIG. 5 is a transverse, cross-sectional view of an evaporator section ofthe flat heat pipe of FIG. 4, corresponding to line V-V thereof.

FIG. 5 is a transverse, cross-sectional view of an evaporator section ofthe flat heat pipe of FIG. 4, corresponding to line V-V thereof.

FIG. 6 is a flowchart showing an exemplary method for manufacturing theflat heat pipe of FIG. 1.

DETAILED DESCRIPTION

Embodiments of the present flat heat pipe will now be described indetail below and with reference to the drawings.

Referring to FIGS. 1-3, a flat heat pipe 1 in accordance with a firstembodiment of the present disclosure is shown. The flat heat pipe 1includes a sealed, flat tube 30, a wick structure 50 lining an innersurface of the tube 30, and working fluid (not shown) contained in thewick structure 50.

The tube 30 is made of metal or metal alloy with a high heatconductivity coefficient, such as copper, copper-alloy, or othersuitable material. The tube 30 is elongated, and has an evaporatorsection 11, an adiabatic section 13, and a condenser section 15 definedin that order along a longitudinal direction thereof. A transversesection of the tube 30 is oval-shaped (or racetrack-shaped). Alongitudinal section of the tube 30 is rectangular.

The wick structure 50 includes a first wick portion 51, a second wickportion 53, and a third wick portion 55. The first wick portion 51 isformed on an inner surface of the evaporator section 11. The second wickportion 53 extends longitudinally from the adiabatic section 13 to thecondenser section 15, and is formed on inner surfaces of the adiabaticsection 13 and the condenser section 15. The second wick portion 53contacts and communicates with the first wick portion 51. The third wickportion 53 is enclosed by the first wick portion 51 and the second wickportion 53. The third wick portion 53 extends longitudinally from theevaporator section 11, and through the adiabatic section 13 to thecondenser section 15, and communicates with the first wick portion 51and the second wick portion 53. A capillary force of the second wickportion 53 is larger than that of the third wick portion 55 and lessthan that of the first wick portion 51. A pore density of the secondwick portion 53 is larger than that of the first wick portion 51 andless than that of the third wick portion 55. In one embodiment, sizes ofthe pores of the first, second and third wick portions 51, 53, 55 areapproximately the same. In such case, the pore density can be measuredaccording to the number of pores per unit area/volume. In otherembodiments, sizes of the pores of any one or more of the first, secondand third wick portions 51, 53, 55 differ. In such cases, the poredensity can be measured according to the total volume of pores per unitarea/volume.

The first wick portion 51 is sintered metal powder, and has the shape ofa flattened annulus. An outer surface of the first wick portion 51 issnugly attached to the inner surface of the evaporator section 11.

The second wick portion 53 is a groove-type wick portion, and a left endthereof connects and communicates with a right end of the first wickportion 51. A length of the second wick portion 53 is larger than thatof the first wick portion 51. The second wick portion 53 includes aplurality of ridges (or elongated teeth) 531 and a plurality of grooves533. Each groove 533 is defined between two corresponding adjacentridges 531.

In the illustrated embodiment, all the ridges 531 are substantially thesame size, and all the grooves 533 are substantially the same size. Atransverse cross-section of each ridge 531 is trapezoidal, and atransverse cross-section of each groove 533 is trapezoidal. A size ofthe transverse cross-section of each ridge 531 is substantially the sameas a size of the transverse cross-section of each groove 533. Each ridge531 tapers from an end thereof far from a center of the tube 30 to anend thereof nearer the center of the tube 30. Each groove 533 tapersfrom an end thereof nearer the center of the tube 30 to an end thereoffar from the center of the tube 30. A transverse width of each groove533 at the end thereof nearer the center of the tube 30 is larger thatof each ridge 531 at the end thereof nearer the center of the tube 30.

The third wick portion 55 is disposed at a middle of one side of thetube 30. A bottom surface of the third wick portion 55 at the evaporatorsection 11 is snugly attached to an inner surface of the first wickportion 51. A bottom surface of the third wick portion 55 at theadiabatic and condenser sections 13, 15 is snugly attached to an innersurface of the second wick portion 53. A top surface of the third wickportion 55 is spaced from the first wick portion 51 and the second wickportion 53. The third wick portion 55 is formed by weaving a pluralityof metal wires such as copper wires and/or stainless steel wires. Alength of the third wick portion 55 is equal to a sum of a length of thefirst wick portion 51 and a length of the second wick portion 53.

In operation, the working fluid at the evaporator section 11 absorbsheat generated by one or more electronic components, and thereby turnsto vapor. The generated vapor moves, carrying the heat with it, towardthe condenser section 15. At the condenser section 15, the vaporcondenses after the heat is dissipated. Because the pore density of thethird wick portion 55 is larger than that of the first wick portion 51,the condensate can rapidly permeate into the third wick portion 55.Because the capillary force of the first wick portion 51 is larger thanthat of the third wick portion 55, the condensate in the third wickportion 55 can be drawn back to the evaporator section 11 rapidly by thefirst wick portion 51. Therefore, the evaporator section 11 of the flatheat pipe 1 avoids becoming dry. Thus, the flat heat pipe 1 has stableand reliable performance.

Referring to FIGS. 4-5, a flat heat pipe 1 a in accordance with a secondembodiment of the present disclosure is shown. The flat heat pipe 1 a issimilar to the flat heat pipe 1 of the first embodiment. However, in theflat heat pipe 1 a, a second wick portion 53 a is formed on the whole ofthe inner surface of the tube 30; and a first wick portion 51 a islocated at the evaporator section 11 and is snugly attached to an innersurface of the second wick portion 53 a.

Referring to FIG. 6, an exemplary method for manufacturing the flat heatpipe 1 includes the following steps:

In step S1, the tube 30 with an open end is provided.

In step S2, the inner surfaces of the adiabatic section 13 and condensersection 15 are etched to form the ridges 531 and the grooves 533, andthus the second wick portion 53 is formed.

In step S3, an amount of metal powder and a mandrel are provided. Themandrel is inserted in the evaporator section 11. A gap is definedbetween an outer surface of the mandrel and the inner surface of theevaporator section 11. The metal powder is filled into the gap. The tube30 with the mandrel and the metal powder is heated at high temperatureuntil the metal powder sinters to form the first wick portion 51. Themandrel is then drawn out of the tube 30. A particle diameter of eachgrain of metal powder is larger than the transverse width of each groove533.

In step S4, a plurality of metal wires is provided and weaved to formthe third wick portion 55. Then the third wick portion 55 is disposed atthe middle of one side of the tube 30, with the bottom surface of thethird wick portion 55 snugly attached to inner surfaces of the firstwick portion 51 and the second wick portion 53, and the top surface ofthe third wick portion 55 spaced from the first wick portion 51 and thesecond wick portion 53.

In step S5, the working medium is injected into the tube 30, the tube 30is evacuated, and the open end of the tube 30 is sealed. In this state,the flat heat pipe 1 is manufactured completely.

A method for manufacturing the flat heat pipe 1 a is similar to that ofthe flat heat pipe 1, except that in step S2, the whole of the innersurface of the tube 30 is etched to form the second wick portion 53 a.Then the first wick portion 51 a is sintered on the inner surface of thesecond wick portion 53 a located at the evaporator section 11,substantially according the third step described above in relation tothe flat heat pipe 1.

It is to be further understood that even though numerous characteristicsand advantages of the present embodiments have been set forth in theforegoing description, together with details of the structures andfunctions of the embodiments, the disclosure is illustrative only, andchanges may be made in detail, especially in matters of shape, size, andarrangement of parts within the principles of the disclosure to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. A flat heat pipe for removing heat from aheat-generating component in thermal contact therewith, the flat heatpipe comprising: a hollow tube comprising an evaporator section, anadiabatic section and a condenser section defined in turn along alongitudinal direction thereof; and a wick structure lining an innersurface of the tube, the wick structure comprising a first wick portionlocated in the evaporator section, a second wick portion located in thecondenser section, and a third wick portion extending longitudinallyfrom the evaporator section, through the adiabatic section to thecondenser section and communicating with the first wick portion and thesecond wick portion; wherein a capillary force of the first wick portionis larger than that of the third wick portion, and a pore density of thefirst wick portion is less than that of the third wick portion.
 2. Theflat heat pipe of claim 1, wherein a capillary force of the second wickportion is larger than that of the third wick portion and less than thatof the first wick portion, and a pore density of the second wick portionis larger than that of the first wick portion and less than that of thethird wick portion.
 3. The flat heat pipe of claim 1, wherein the thirdwick portion is enclosed by the first wick portion and the second wickportion.
 4. The flat heat pipe of claim 3, wherein the third wickportion is disposed at a middle of one side of the tube, a bottomsurface of the third wick portion at the evaporator section is snuglyattached to an inner surface of the first wick portion, a bottom surfaceof the third wick portion at the adiabatic and condenser sections issnugly attached to an inner surface of the second wick portion, and atop surface of the third wick portion is spaced from the first wickportion and the second wick portion.
 5. The flat heat pipe of claim 1,wherein the second wick portion extends longitudinally from theadiabatic section to the condenser section, and is formed on innersurfaces of the adiabatic section and the condenser section.
 6. The flatheat pipe of claim 5, wherein the first wick portion is formed on aninner surface of the evaporator section, and an inner end of the firstwick portion contacts and communicates with an inner end of the secondwick portion.
 7. The flat heat pipe of claim 1, wherein the second wickportion is formed on the whole of the inner surface of the tube, and thefirst wick portion is formed on an inner surface of the second wickportion.
 8. The flat heat pipe of claim 1, wherein the first wickportion comprises sintered metal powder.
 9. The flat heat pipe of claim1, wherein the second wick portion is a groove-type wick portion. 10.The flat heat pipe of claim 9, wherein the second wick portion includesa plurality of elongated ridges and a plurality of grooves, and eachgroove is defined between two corresponding adjacent ridges.
 11. Theflat heat pipe of claim 1, wherein the third wick portion is formed byweaving a plurality of metal wires.
 12. The flat heat pipe of claim 1,wherein a length of the third wick portion is equal to a sum of a lengthof the first wick portion and a length of the second wick portion.
 13. Amethod for manufacturing a flat heat pipe, the method comprising:providing a hollow tube comprising an evaporator section, an adiabaticsection and a condenser section defined in turn along a longitudinaldirection thereof; etching an inner surface of the condenser section toform a plurality of ridges and a plurality of grooves, each groovedefined between two corresponding adjacent ridges, the ridges and thegrooves cooperatively forming a second wick portion; providing an amountof metal powder and a mandrel, inserting the mandrel in the evaporatorsection such that a gap is defined between an outer surface of themandrel and the inner surface of the evaporator section, filling themetal powder in the gap, heating the tube with the mandrel and the metalpowder until the metal powder sinters to form a first wick portion, andthen drawing the mandrel out of the evaporator section; and providing aplurality of metal wires and weaving the metal wires to form a thirdwick portion, the third wick portion extending longitudinally from theevaporator section, through the adiabatic section to the condensersection and communicating with the first wick portion and the secondwick portion; wherein a capillary force of the first wick portion islarger than that of the third wick portion, and a pore density of thefirst wick portion is less than that of the third wick portion.
 14. Themethod of claim 13, wherein when the inner surface of the condensersection is etched to form the plurality of ridges and the plurality ofgrooves, inner surfaces of the adiabatic section and condenser sectionare also etched, such that the plurality of ridges and the plurality ofgrooves are formed in the condenser section, the adiabatic section andcondenser section.
 15. The method of claim 14, wherein the first wickportion is directly formed on the inner surface of the evaporatorsection.
 16. The method of claim 14, wherein the whole of the innersurface of the tube is etched.
 17. The method of claim 16, wherein thefirst wick portion is formed on an inner surface of the second wickportion.
 18. The method of claim 17, wherein a particle diameter of eachgrain of metal powder is larger than the transverse width of eachgroove.